In various industries, such as aluminum smelters, high amounts of spent potlining or other leachates are contaminated with stable metal cyanides, typically compounds containing the ferro-cyanide complex ions. The management of these industrial by-products is expensive requiring secure containment mechanisms to prevent cyanide leachate migration or runoff. This is of grave environmental concern to the inventors and to society at large. The present invention consists of destroying CN contained in these compounds, by electrochemical oxidation in an inexpensive and energetically economical manner.
U.S. Pat. No. 3,816,275 describes a process for the treatment of waste liquors containing a cyano-complex such as ferricyanide by electrolysing the liquor using an iron anode thereby forming ferrocyanide or a ferricyanide ion containing complex salt, both of which form a blue colloid of Prussia Blue and surface in the liquor to form a scum which is separable from the remaining of the waste liquor.
WO 01/62993 describes a process for recovery of cyanide by electrochemical dissociation of the metal-cyanide complex and electrowinning of the metal while the free cyanide generated in the process is recovered in a membrane.
Szpyrkowicz et al. (Annali di Chimica, 93, 2003) describes electrochemical oxidation to destroy cyanide in wastewaters of copper plating, using various anode materials (Ti/Pt, Ti with various oxides, and stainless steel) anode and stainless steel cathode in alkaline solution. The presence of a copper oxide on the anode is postulated.
Wo 98/18982 describes an alkaline electrolytic bath for transformation of a cyanidric brass bath into a non-cyanidric one, thereby allowing the deposition of brass without contamination of the washing waters with cyanide.
Furthermore, there is extensive literature on the recovery of cyanide for metal plating or gold production or relating to the destruction of CN− ion. However, the present invention is suitable for the destruction of the more stable metallic cyanide complexes, as well as the CN− ion.